This invention relates to a process for preparing overcoated electrophotographic imaging members and more particularly, to a process of preparing electrophotographic imaging members overcoated with a solid cross-linked organosiloxane colloidal silica hybrid polymer.
The formation and development of electrostatic latent images utilizing electrophotographic imaging members is well known. One of the most widely used processes being xerography as described by Carlson in U.S. Pat. No. 2,297,691. In this process, an electrostatic latent image formed on an electrophotographic imaging member is developed by applying electroscopic toner particles thereto to form a visible toner image corresponding to the electrostatic latent image. Development may be effected by numerous known techniques including cascade development, powder cloud development, magnetic brush development, liquid development and the like. The deposited toner image is normally transferred to a receiving member such as paper.
There has recently been developed for use in xerographic imaging systems and for use in imaging systems utilizing a double charging process as explained hereinafter, overcoated organic imaging members including layered organic and layered inorganic photoresponsive devices. In one such photoresponsive device, a substrate is overcoated with a hole injecting layer, which in turn is overcoated with a hole transport layer, followed by an overcoating of a hole generating layer, and an insulating organic resin overcoating as a top coating. These devices have been found to be very useful in imaging systems, and have the advantage that high quality images are obtained, with the overcoating acting primarily as a protectant. The details of this type of overcoated photoreceptor are fully disclosed by Chu et al in U.S. Pat. No. 4,251,612. Similar multilayer photoreceptors are described, for example, in U.S. Pat. No. 4,265,990. The entire disclosures of these two patents are incorporated herein by reference.
Other photoreceptors that may utilize protective overcoatings include inorganic photoreceptors such as the selenium alloy photoreceptors, disclosed in U.S. Pat. No. 3,312,548, the entire disclosure of which is incorporated herein by reference.
When utilizing such an organic or inorganic photoresponsive device in different imaging systems, various environmental conditions detrimental to the performance and life of the photoreceptor from both a physical and chemical contamination viewpoint can be encountered. For example, organic amines, mercury vapor, human fingerprints, high temperatures and the like can cause crystallization of amorphous selenium photoreceptors thereby resulting in undesirable copy quality and image deletion. Further, physical damage such as scratches on both organic and inorganic photoresponsive devices can result in unwanted printout on the final copy. In addition, organic photoresponsive devices sensitive to oxidation amplified by electric charging devices can experience reduced useful life in a machine environment. Also, with certain overcoated organic photoreceptors, difficulties have been encountered with regard to the formation and transfer of developed toner images. For example, toner materials often do not release sufficiently from a photoresponsive surface during transfer or cleaning thereby forming unwanted residual toner particles thereon. These unwanted toner particles are subsequently embedded into or transferred from the imaging surface in subsequent imaging steps, thereby resulting in undesirable images of low quality and/or high background. In some instances, the dry toner particles also adhere to the imaging member and cause printout of background areas due to the adhesive attraction of the toner particles to the photoreceptor surface. This can be particularly troublesome when elastomeric polymers or resins are employed as photoreceptor overcoatings. For example, low molecular weight silicone components in protective overcoatings can migrate to the outer surface of the overcoating and act as an adhesive for dry toner particles brought into contact therewith in the background areas of the photoreceptor during xerographic development. These toner deposits result in high background prints.
When silicone protective overcoatings such as polysiloxane resins are used on selenium photoreceptors, particularly photoreceptors having low arsenic content, undesirable crystallization of the vitreous selenium can occur. This crystallization may result from the elevated temperatures used to cure the coating. When room temperature curing catalysts are used for curing silicones such as organic amine catalysts, the presence of the catalysts in the overcoating can crystallize the vitreous selenium over a period of time.
Moreover, catalysts in silicone overcoatings for photoreceptors having charge transport and charge generating layers often cause degradation of the photoreceptor. For example, organic amine catalysts having a solvating effect on polycarbonate binders for photoreceptors which in turn causes penetration into the binder layer with undesirable degradation of the photoconductive properties.
Further, silicone overcoatings, particularly those that cure at room temperature, often require long curing times of about 48 hours or longer. Long curing times adversely affect productivity and prolongs the period during which the overcoating is sensitive to physical and chemical damage.